1. Field of the Invention
This invention relates to a method and apparatus for conveying developing agent, or developer. More particularly, it is concerned with a method and an apparatus capable of readily conveying magnetic developer for developing a latent image on an image bearing member.
2. Description of Prior Arts
There have heretofore been proposed various types of image forming device which form and utilize a developed image. Such image forming devices have been in practical use.
Widely used in particular is a type, in which an electrostatic latent image is formed on a photosensitive member based on the electrophotographic method, and the latent image is developed for the image formation. Besides this, there have also been used a system, in which an electrostatic image is formed on an insulative surface in accordance with a signal from an electrostatic pin electrode, or a system, in which an electrostatic latent image is formed on a screen photosensitive member having therein a multitude of openings, and then ion current is modulated in accordance with the latent image, thereby forming an electrostatic image on an insulative surface, followed by its development for the image formation.
In the image forming device of a type, in which a developed image is obtained by use of a developer, disposal of the developer constitutes an important factor for the operating efficiency of the device. In particular, when an image bearing member, on which a developed image is formed, is repetitively used, such disposal becomes significant from the standpoint of recovery and re-use of the developer.
It has so far been the practice that the developer which remains after the image transfer operation on the image bearing member in the above-described type of image forming device is separated and removed from the image bearing member by a cleaning device such as a blade, a fur brush, a web, and so forth.
In the case of the web cleaning, the removed developer is adhered onto the web, which functions as a conveyor for the developer, as it is moved by a forwarding mechanism at the time of the cleaning. The transportation of the developer by the web, however, requires a driving mechanism for unwinding and winding of the web, and also necessitates, along with such mechanism, a considerable amount of space for the web to be unwound and wound after recovery of the developer. Moreover, re-use of the developer adhered onto the web is difficult in that separation of the developer off the web is fairly troublesome, and fabrics constituting the web are liable to mix the developer as separated therefrom.
In the case of the fur brush cleaning, there has been widely practiced that the removed developer is conveyed into a filter pack from the cleaning section by a suction mechanism through a conveying duct. When using the suction mechanism, however, a high-powered suction fan or impeller is required for obtaining sufficient suction force, hence it is inevitable that the suction mechanism becomes large in size to occupy a considerable space. Furthermore, re-use of the developer accumulated in the filter pack is difficult as is the case with the web cleaning.
In the case of the blade cleaning, there has been adopted such a construction that a cleaning blade is provided at the side surface of the photosensitive drum, the developer as scraped off the drum surface is recovered into a receptacle provided at the lower part of the drum by gravity, and then it is discharged sidewise by means of a screw conveyor. There has also been adopted such a construction that the cleaning blade is disposed at an upper part of the photosensitive drum, a guide member is contiguously provided to the cleaning blade, and the removed developing agent is discharged sidewise by a screw conveyor disposed in a space gap formed by the blade and the guide member. The developer as discharged sidewise in the above-described manner is guided to a receptacle provided at a lower position by gravity fall, for recovery and re-use.
While utilization of gravity is preferable in that no driving source for the conveying device is required, the direction for the recovery is limited to the downward direction accompanied by a considerable space for the gravity fall of the removed developer, hence its range of utility has been limited to some extent. In addition, there is apprehension such that the falling developer is liable to scatter in all directions to adhere to the surface of the photosensitive body or other process means, hence preventive measures there against should be taken in some occasion. In particular, when the electrophotographic device is to be miniaturized in size, the abovementioned limitation brings about a serious obstacle which could not be expected in a large-sized device.
While the screw conveyor is compact in size and shape as the conveying device, as it operates to convey the material under pressure of the screw disposed within a groove or tubing, it is disadvantageous in that the removed developer is liable to be solidified in transit. Besides the screw conveyor, there can be contemplated a system of circulatory movement of a number of buckets, or a belt conveyor system. These systems, however, require unavoidably a returning path for the circulating buckets and belt with the consequence that a considerable space is necessary including the driving mechanism therefor.